page_title: Ring chromosome 18
section_title: Research
hierarchical_section_title: Ring chromosome 18 / Research
caption_attribution_description: Corpus callosum from above.
context_page_description: Ring chromosome 18 is a genetic condition caused by a deletion of the two ends of chromosome 18 followed by the formation of a ring-shaped chromosome. It was first reported in 1964.
context_section_description: Currently, research is focusing on identifying the role of the genes on 18p and 18q in causing the signs and symptoms associated with deletions of 18p and/or 18q.  This will ultimately enable predictive genotyping. Thus far, several genes on chromosome 18 have been linked with a phenotypic effect.
  TGIF - Mutations and deletions of this gene, which is located on18p, have been associated with holoprosencephaly.  Penetrance is incomplete, meaning that a deletion of one copy of this gene is not in and of itself sufficient to cause holoprosencephaly.  Ten to fifteen percent of people with 18p- have holoprosencephaly, suggesting that other genetic and environmental facts play a role in the etiology of holoprosencephaly in these individuals.
  TCF4 – In 2007, deletions of or point mutations in this gene, which is located on 18q, were identified as the cause of Pitt-Hopkins disease.  This is the first gene that has been definitively shown to directly cause a clinical phenotype when deleted.  If a deletion includes the TCF4 gene (located at 52,889,562-52,946,887), features of Pitt-Hopkins may be present, including abnormal corpus callosum; short neck; small penis; accessory and wide-spaced nipples; broad or clubbed fingers; and sacral dimple.  Those with deletions inclusive of TCF4 have a significantly more severe cognitive phenotype.
  TSHZ1 - Point mutations and deletions of this gene, located on 18q, are linked with congenital aural atresia  Individuals with deletions inclusive of this gene have a 78% chance of having aural atresia.
  Critical regions – Recent research has narrowed the critical regions for four features of the distal 18q- phenotype down to a small segment of distal 18q, although the precise genes responsible for those features remain to be identified.
  Haplolethal Regions - There are two regions on chromosome 18 that has never been found to be deleted.  They are located between the centromere and 22,826,284 bp (18q11.2) and between 43,832,732 and 45,297,446 bp (18q21.1).  It is hypothesized that there are genes in these regions that are lethal when deleted.
caption: corpus callosum
exif: {}